Many corona charging units of the prior art are fixedly mounted so that no adjustment of the corona wire is possible. Other arrangements include mounting hardware for the corona housing wherein the entire housing is moveable to adjust the wire relative to the photoconductive surface. The housing in such latter arrangements limits the span of adjustment available. In addition, it is frequently important that the corona housing remain in a relatively fixed position to minimize contamination of the corona by toner particles, dust or the like, which can be defeated by requiring adjustment of the entire housing. Still further, many contemporary corona units include multiple corona wires within a common housing so that adjustment of a housing position for one wire is not likely to result in an ideal adjustment for other wires in that same housing.
Still other prior art corona devices have been developed for the purpose of allowing wire adjustment without moving the housing. For instance, U.S. Pat. No. 4,089,600 to Ito et al describes a corona wire adjuster which employs a set screw threaded through one leg of an L-shaped member, the other leg of which has a notch which engages the corona wire. Turning the set screw moves the L-shaped member, and the engaged corona wire. This corona wire adjuster requires at least two parts (i.e., the set screw and the L-shaped member) and requires their alignment before assembly in the corona charging apparatus. Further, the set screw must be driven into its mounting, to a nominal or reference position, prior to adjusting the corona wire, and can only be moved one way from the nominal position.
Another corona wire adjuster allowing wire adjustment without moving the housing is described in U.S. Pat. No. 3,922,548 to Honda. It employs a corona wire mounted on a rail supported by leaf springs and movable by a pair of set screws. At least three parts (i.e., the rail, the set screws and the leaf springs) are required. For assembly these parts must be aligned and the set screws driven to a nominal or reference position.